FIG. 1 is a side view of a typical railway vehicle. As shown, the railway vehicle 1 is made so as to travel on rails 3, and has a basic structure made up of wheels 2, trucks 4, a vehicle body 5, and accessories.
The vehicle body 5 is a portion that is used to transport passengers, forms a shape of the vehicle, and exists in various types according to the purpose. The railway vehicle 1 is divided into various types such as locomotives, passenger vehicles, and freight vehicles.
The wheels 2 are each formed of special steel, and are fixed to respective opposite left and right hand ends of an axle 6. Typically, two pairs of wheels 2 are coupled to construct one truck 4. In the case of the locomotive, three or more pairs of wheels 2 may be installed on one truck 4. Further, two trucks 4 are generally installed on one railway car.
Each truck 4 is configured to be coupled with the vehicle body 5 at the middle part thereof by a pin so as to be able to rotate relative to the vehicle body 5 at a predetermined angle. This is intended to cause the trucks 4 coupled to the same vehicle body 5 to have rotatability when fitted to the curvature of the respective rails 3 during curved movement.
Each wheel 2 plays a crucial role in the safe service and the running speed of the railway vehicle. The wheel 2 is structurally made up of a wheel tread 22 that is in rolling contact with a top surface of the rail 3, and a wheel flange 21 corresponding to a step protruding from the wheel tread 22 in order to prevent derailing during curved movement.
Each truck 4 is a part which supports the vehicle body 5 and on which the axle 6 and the wheels 2 are installed. Each truck 4 should have a bearing force capable of withstanding high-speed operation and load, and be equipped with suspension including a damping device and braking devices. Generally, one of the most difficult problems with truck design for the railway vehicle 1 is that two contradictory requirements must be satisfied, that is, the truck 4 must enable the railway vehicle 1 to move safely at high speed while moving on straight rails, and prevent the vehicle from derailing while moving on curved rails.
FIG. 2 is an explanatory view showing the cause of squealing noise. FIG. 3 is a side view showing a contact surface of a wheel flange 21 and a rail 3 in the related art. Referring to FIGS. 2 and 3, due to a centrifugal force generated when the railway vehicle 1 moves along a curve, the danger of the vehicle derailing is increased, and the wear of the wheels 2 or the rails 3 is increased. Thus, the maintenance expenses of the rails 3 are increased. Further, the squealing noise generated greatly reduces the riding comfort.
When the railway vehicle 1 moves along a curve, a transverse load is generated due to the centrifugal force. The transverse load greatly increases frictional forces Fx and Fz on a contact surface of a lateral surface 3d of the rail 3 and the wheel flange 21. The frictional forces are transmitted to passengers as “screechy” high-frequency noise. The frictional forces Fx and Fz greatly increased by the centrifugal force compared to the straight moving wear down the wheels 2 or the rails 3 on curved portions, and cause a severe squealing noise.
This problem increases in proportion to the centrifugal force, and becomes more serious when a high-speed train moves along the curved rails 3 or when the curvature of the curve is very great, even in the case of a low-speed train such as a subway train.